src: use internal/errors for startSigintWatchdog

Move the throw out of c++ and into js using internal/errors

PR-URL: https://github.com/nodejs/node/pull/16546


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>